Control device



1941- w. CHRISTIANSEN 2,266,721

CONTROL DEVICE Filed Oct. 24, 1938 E o o I q INVENTOR.

Z4, 8 ATTORNEY.

Patented Dec. 16, 1941 CONTROL DEVICE William Christiansen, Milwaukee, Wis, assignor to Perfex Corporation, Milwaukee, Wis., a corporation of Wisconsin Application October 24 1938, Serial No. 236,818

31 Claims.

This invention relates in general to control devices, and'more particularly to oil burner control devices. a

In oil burner control systems, it is customary to provide some device which will, in case of ignition failure or flame failure, shut the oil burner down until such device has been manually reset. Such a device is generally referred to as a safety switch and usually consists of a pair of contacts, a bimetal actuator and an electric heater for the actuator. Such a safety switch is often referred to as a lockout switch. Usually the safety switch heater is energized upon starting the oil burner and then after combustion has been established the heater is deenergized. The means for deenergizing the safety switch heater is usually responsive to combustion conditions and is generally referred to as a combustion responsive switch or stack switch.

This stack switch usually consists of a driving member in the form of a thermal element couoperation of the various parts and elements which will be hereinafter more fully described in the specification and particularly pointed out in the appended claims and of which a preferred embodiment is illustrated in the accompanying sheet of drawings. Referring to. the drawing:

Fig. 1 is a cross sectional side elevation of a stack switch incorporating various novel features of the invention;

pied to a driven member in the form of an actuating arm. The latter member is arranged to move only a limited amount and to operate switch contacts for controlling the lockout switch heater or for performing other additional control functions when desired. The coupling means is usually a slip friction device which consists basically of two frictionally engaged elements. The two elements move together as a unit so long/as the actuating arm is free to move, but slide relative This permits con-' Another objectof this invention is to provide a a new and improved thermal element for a control device.

Another object of this invention is to provide a new and improved slip friction mechanism for a control device.

Another object of this invention is to provide a method of manually adjusting the combustion responsive device or stack switch to match the thermal characteristics of the system with which it'is used.

Other objects and advantages reside in certain novel features of construction, arrangement and Fig. 2 is'a cross section through the thermal element taken along the line 22 of Fig. 1;

Fig. 3 is a cross, section taken along the line 3-3 of Fig. 1 showing the switching arm;

Fig. 4 is a cross section of the switch taken along the line 4-4 of Fig. 1 and showing the slip friction mechanism; while,

Fig. 5 is a cross section taken along the line 5-5 of Fig. 1 showing the switch arm adjusting means.

General description Referring now particularly to Fig. 1, the control device comprises a physical condition responsive means such as a thermal device having a plurality of elements. One of these elements has a relatively high coefficient of expansion and is made of heat resisting material, and preferably constructed as shown in the drawing of an elongated channel member formed into a U-shape to provide a pair of substantially parallel channel portions 6. The open ends of the U are rigidly fastened by rivets 8 to lugs 7 cast integral with a support plate 8. The second'of these elements has a relatively low coefficient of expansion and is shown in the drawing as a tubular element ID made of heat resisting material. This element is rigidly fastened at one of its ends to the U- bend or free end of the expansive element 6 by a rivet H.

The other end of the low expansive element I0 is slotted and flattened as shown, and is also arranged to protrude through a guide or bearing opening I! in'the support plate 8. A straight line slip friction means is provided which includes a connector link shown in the drawing as a spring blade l4 preferably constructed of hard, smooth corrosion resisting material such as stainless steel which is secured to the protruding'end of the low expansive element It by means of a rivet, l3.

staked at one end to the support plate 8 is a support tube It for receiving a mounting flange H! which is held rigidly thereto by a flange set screw 20. The support 8 is fastened rigidly to a base plate 22 by means of screws 24. Hinge supports or lugs '26 (Fig. 4) cast integral with elements.

- friction block bracket 38.

the support 8 protrude through the base 22 to receive a hinge member shown in the drawing as a U-shaped spring hinge 28. The open ends of the U spring hinge 28 are clamped between a hinge clamp 38 and the hinge supports 25 by screws 32 which pass through the two former members and thread into the latter. The base 1 portion of the U-shaped spring hinge 28 is clamped between a movable member shown as an actuating or control arm 34 and a friction block in the form of a bracket or clamping plate 36 by means of rivets 38. The slip friction means previously pointed out includes two additional One of these comprises a block of friction material 48 preferably made ofcarbon and inserted in a cavity or recess formed in the ing effort on blade 14 is'applied by an adjustable means such as a screw d8 threaded through the actuating arm 34 and bearing upon a compression spring 50 which is set at such an angle that its horizontal component of force is always sufficient to cause the friction block support 84 to bear against but one side of the guide pins 46. One end of the compression spring 58 extends into a recess 52 formed in a boss 53 on the friction block support 44, and the other end receives a cup-shaped insert 58 which in turn receives the tipof the screw 48.

A biasing spring shown in the drawing as a compression spring 56 is inserted between the actuating arm 34 and the base 22. One end of the spring 56 if. slipped over a pin 58 staked to the actuating arm 34. and the other end is slipped over a cupped washer 50. An adjusting screw 8-2;" threaded through the base 22 and locked in place by a nut 64, extends into a recess in the cupped washer 68 and serves to adjust the effort of biasing spring 58 on the actuating arm 34. An insulating member 66 is fastened to the actuating arm 34 by means of screw 68 and serves to further amplify the relative motion of the thermal elements. The insulating member 88 carries a metal plate which is fastened to it by rivets 12. Two switch actuating screws I4 and 16 are tightly but adjustably threaded -into the plate l0. A cover plate 18 for the various elements is fastened to the base 22 by screws 80. Suitably fastened to, but insulated from, the cover 18 is a pair of cold spring contacts 82 operated by the screw'IB. Also suitably fastened to but insulated from the base 22 is a pair of hot spring contacts 84 operated by the screw 14. A fixed cold stop 88 is secured to the cover 18 for limiting the motion of the actuating arm assembly in the cold or outward direction. A manual adjusting arm 88 is pivotly fastened to the cover 18 by means of a rivet 92 and a spring washer 94.

strain free by frictionally holding the arm 88 in its ad usted Q3163 spring washer 94 serves to reposition.- Fixed to adjusting arm 88 and operating through a curved slot 96 in the cover 18 1s The other of these The support 44 is arranged to freely ovement of the adjusting arm 88 Operation The operation of the control device in its preferred formwill now be described in detail. The control device is usually mounted by means of the supporting flange 18, with the thermal elements 6 and ll] extending into the stack of an oil burning furnace, although it may be mounted anywhere where it will be subjected to combustion conditions within the temperature range of the thermal elements. Fig. lillustrates the control in the cold position, showing the actuating arm assembly 34 and 66 resting against the cold stop 86 and the switch actuating screw 18 holding the; cold spring contacts closed. When combustion is established in-the burner the thermal elements 6 and 18 are heated, due to the elevated temperature of the hot gasses passing over them. The U-shaped element 6 expands relatively .more than the tubular element i8 and causes the latter element and the spring blade Hi to move to the left relative to the support plate 8. This motion is imparted to the actuating arm 34 through the friction blocks 48 and 42 and causes it to rotate in a counterclockwise direction about a point in the spring hinge 28 and results in imparting amplified motion to the insulating member 66 and its associated parts in a direction away from the cold stop 86 and toward the base 22. As this motion continues, responsive to the increasing temperature of the thermal elements 8 and it, the switch actuating screw 76 opens the .cold contacts 82 at one position of the insulating member 66, the switch actuating screw M closes the hot contacts 84 at another position of the insulating member 68 and finally the insulating member 66 reaches the hot stop 98 at the end of its travel.

Further motion of the thermal elements 6 and it due to additional temperature rise cannot result in further motion of the actuator arm assembly 38 and 86 because of the restriction by the hot stop 98 and relative motion between. T

the friction blocks 413 and 42 and the spring blade l4 ensues. The spring blade l4 slips between the lated by the pressure of the friction blocks and 42 on the spring blade 14 and this in turn is regulated by the adjusting screw 48 through the compression spring 50. Determination of the correct amount of slip effort is made after consideration of the load to be carried by the actuating arm assembly. It is obvious that the slip effort must be sufiiciently high to carry the useful load, but not high enough to cause deformation of any of the links in. the mechanism.

Assume now that for some reason the stack temperature starts to drop. Upon initial contraction of the thermal elements the actuator arm assembly 34 and 66 moves away from the base 22 and the "hot stop 98. As motion in this direction continues the switch actuating screw 14 opens the hot contacts 84 in one position, the actuating screw l6 closes the cold" contacts 82 in another position, and finally the insulating member. encounters the cold" stop 86 at the end of its travel. Further motion of the thermal elements 6 and rection causes the spring blade l4 to slide or slip between the friction blocks 40 and 42 in the same manner as has been described, but in this case the movement or operation is in the opposite direction. The device therefore operates uponchanges in temperature independent of actual temperature.

It should be understood from the. foregoing explanation that the slip friction mechanism performs several functions. In addition to serving as a means for transmitting relative motion of the thermal element to the actuating arm, it functions in such a manner that movement of the actuating arm is initiated upon initial relative movement of the thermal elements in either direction, and that continued relative motion of the thermal elements is permitted without excessive strain to the mechanism although the actuating arm is restrained. g

The reason for placing the spring 50 at an angle with respect to fridtion block support 44 can now be better understood in the light of the preceding explanation. In order that the friction block support 44 might move freely on the guide pins 46 tween the guide pins 46 and the guide holes in the friction block support 44. If effort were applied normal to the the slip effort obtained, during the time the friction block support either side of the guide pins, would be that due to the friction between the spring blade and the top friction block 40 alone, since the bottom block 42 would move with the spring blade l2. Now when the bottom friction block support 44 engages the guide pins, the slip effort would increase to twice the former value for then the slip effort would be due to the friction between both the friction blocks and the spring blade. By placing the spring 50 as shown and applying the force to the blocks at an angle to the direction of the guide pins, a component of force normal to the guide pins of sufficient magnitude is obtained which is in excess of one-half of the total slip efiort. This force keeps the friction block support 44 tightly against the guide pins at all times and maintains the slip effort constant.

This control device has universal application and consequently may be mounted into stacks of vastly different characteristics. In some instances the stack temperature may fluctuate widely from its maximum value although combustion conditions are entirely safe. In other instances a wide fluctuation in stack temperature is indicative of dangerous conditions. In order that the control will not falsely shut down the system in the former instance and will shut down systeminthe latter instance thecontrol must be capable of adjustment to match the characteristics of such unusual installations.

The distance the stack arm. assembly must travel from the hot stop to-open the hot contacts determines the amount the stack temperature must decrease from its maximum value in order to open the hot contacts. Therefore, by adjusting the position of the hot stop the necessary decrease in stack temperature to shut down the control may be set. That is, if large stack plane of the friction blocks temperature fluctuations may be tolerated the ID in the "cold dithere must be some clearance bea 44 was not bearing againstv 4 the cold arm 88 is moved all the way to the right moving the hot stop 98 closer to the base 22 and allowing the stack arm assembly 34--66 to travel its maximum amount. If, however, only small stack fluctuations may be safely tolerated the adjusting arm 88 is moved farther to left, moving the hot stop 98 away from the base and allowing the stack arm assembly 34--66 to travel a smaller amount. The biasing spring 56 is a safety link which serves to move the actuating arm assembly into position in the event of failure of the actuating linkages.

a The perforated washer I 00 enclosing the end of the suppcrttube It serves as a shield to prevent the passage-of the stack gasses into the cover 18, or to prevent the passage of cold air into the stack over the thermal elements 6 and l0.

A plane passing through the two sides of the U-shaped channel element 6 extends at an oblique angle to a vertical plane when the control.

is mounted in its normal position. This method of mounting the thermal element is used for the following reason: Usually the control is mounted so as to have the thermal element extend into either a horizontal or vertical stack. By mounting the U-shaped element at approximately a 45 angle one element of the thermal device does not completely overshadow and shield another element and thereby prevent free passage of the stack gasses over all the elements.

The stack elements 6 and I0 extend at right angles and perpendicularly from the rear of the base while the slip friction mechanism extends axially of the stack elements and perpendicularly from the front of the base, The effort of the stack elements is, therefore, along a straight line longitudinal of the elements so that the actuating arm is moved in a direction toward and away from the base. of the actuating arm is greatly amplified due to the closeness of the position of'its pivoting spring hinge on the base'to the slip friction mechanism.

An important feature of the invention concerns the construction of the channel and tube sensitive element for the stack switch. The thermal device when so constructed is very strong structurally although it has a high ratio of heat,

receptive surface area, to heat absorbing mass and consequently is able to follow relatively rapid temperature changes.

While the drawing discloses only the preferred form of invention, obviously the device would have the same utility if its essential elements were arranged in reversed manner. For example, it may be desirable to construct the tubular member H) of relatively high expansive material and the U-shaped channel member 6 of relatively low expansive material, or it may be desirable that the carbon friction blocks 40 and 42 be fastened to the tubular member ID instead of to the actuating arm 34 and the spring blade H be fastened to the actuating arm' 34 instead of the tubular member l0.

While the drawing discloses the utility of the device as an electrical switch operating means, it should be understood that the. device may be arranged to perform additional mechanical functions as well.

While a specific embodiment of the invention has been disclosed and described, it will be apparent that many changes or modifications in the specific details of the elements can be made without departing from the spirit of the inven- The movement of the free end tionpand it is therefore desired that the invention belim'ited only by the scope of the appended claims:

What is claimed is:

1. A control mechanism comprising, an elongated thermal deViceQa control arm, a slip friction connection between the thermal device andthe control arm, said thermal device comprising a pair of channel members and atube having relatively different coeficients of expansion, means for securing one end of the channel members to motion of the control arm whereby the initial of the arm, and slip friction means connecting the thermal element to the actuating arm thru which initial relative motion between the chan-. nel and tube is imparted to the actuating arm.

3, A control device comprising an elongated thermal device having a plurality of elements extending into a fluid operating medium for actuating the same, an actuating arm, a pair of stops for limitin the movement of the arm, a base, slip friction means extending perpendicular to the base an through which motion of the thermal device is imparted to the actuating arm until the stops are encountered, a support plate on the base having lugs for supporting one end of the thermal device, said lugs supporting said thermal device at an. oblique angle to a plane perpendicular to the plane of the baseand parallel to one edge of the base whereby one element of the thermal device does not completely shieldanother element from the free passage of the operating fluid medium over all elements.

4. In a control device comprising at least two elongated thermal members each having a different coefficient of expansion and contraction,

said elongated members arranged in parallel relationship, a support plate, means for rigidly securing the end of one of said members to the support plate, the end of said other member extending through said support plate, means for rigidly securing the other ends of said members together at a point remote from the support plate, said members extending in a horizontal direction from the plane of the support plate and arranged at an oblique angle with respect.

to a vertical plane thru said members whereby both members are freely and concurrently afiected by line gasses traveling in either a vertical or horizontal direction.

5. In a' control device of the classdescribed, a thermal element comprising a pair of elongated members each havinga difi'erent coeflicient of expansion and contraction and actuated by a actuated by the members.

one end of the tube and means for limiting the relative motion between the tube and channel by thefiuid medium passing overthe members in a direction at right angles thereto, said members also arranged at an oblique angle with respect to the passage of the fluid medium whereby the fluid medium has free access to both of said members concurrently and the members are uniformly rendered effective, and control means 6. In a control device of the class described, a physical condition responsive means including a relatively expansible element and a relatively non-expansible element associated therewith, a support plate, said non-expansible element comprising an elongated tubular member extending p. freely thru said support plate, said expansible element comprising an elongated channel shaped member bent into a U-shape, means for securing the ends of the channel member to said support plate, means for securing the U-bent portion of the channel member to one end of the tubular member whereby relative movement of the members is effective to cause a movement of the free end of the tubular member.

'7. In a control device of the class described, a thermal responsive means including a relatively expansible element and a relatively non-expansible element associated therewith, a support plate, said non-expansible element comprising an elongated tubular member extending freely thru said support plate, said expansible element comprising an elongated channel shaped member bent into a U-shape, means for supporting the ends of the channel member from the support plate, said tubular member arranged parallel to and between the sides of the U-shaped channel member,means for securing one end of the tubular member to the U-bent portion of the channel member whereby relative movements of said members is efiective to cause a movement of the free end of the tubular member, switching means arranged upon said support plate, and means connecting the free end of the tubular member with the switching means for operating the same.

8. A control mechanism of the class described comprising an elongated thermal device ncluding a channel member formed into a U-shape and a tube member fastened to the U-shaped channel plate and arranged in parallel relationship .to'

each other, means for mounting said members horizontally and in a position to be acted upon member at the bend in the U, a base, an actuating arm, a tubular support having staking lugs, a spring hinge, slip friction means fastened to the spring hinge and the thermal device for imparting the motion of the thermal device to the actuating arm, a support plate having lugs on one side to receive the channel member, lugs on the other side of the support plate for receiving the .spring hinge, and a flange on-the support plate between the lugs to fasten the base thereto, said support plate having a hole extending therethru for loosely guiding the tubular member, said support plate having a series of small holes extending therethru forreceiving the staking lugs on the tubular support.

9. A control mechanism comprising a thermal device having two ends, an actuating arm, a support for one end of the thermal device, a slip friction means connecting the actuating arm with the free end of the thermal device, aid slip friction means including a spring hin e for hinging the actuating arm to the thermal evice support, a block offriction material rigidly fastened to the actuating arm, a second block of friction material adjustably secured to the actuating arm, a spring blade frictionally engaged between the actuating arm,

both of said friction blocks and fastened on the free end of the thermal device, and means for applying compressive force to the friction blocks to regulate the frictional slip effort of the spring blade with reference to the actuating arm.

10. A control device of the class described comprising a physical condition responsive means, an actuating arm, a pair of stops for the arm, a base, a straight line slip friction mechanism comprising three flat elements with one element resiliently clamped between the other two for connecting the actuating arm to the physical condition responsive means whereby motion of the physical condition responsive means is imparted to .the actuating arm, switching means fastened to the base, an insulating member fastened to the actuating arm, and an adjustable switch operator supported on the insulating member whereby motion of the actuating arm is imparted to the switching means.

11. In a control device of the class described, physical condition responsive means, a support plate, means for supporting one end of said condition responsive means on said support plate, a spring blade secured to the free end of said condition responsive means, an actuating arm, friction means carried by said actuating arm and engaging each side of said spring blade, means for hingedly pivoting said actuating arm from said support plate, said condition responsive means effective upon an initial movement thereof to move said actuating arm about its hinge support through the medium of said spring blade,

stop means for limiting the movement of said actuating arm, said spring blade effecting a slip- Dage movement between said friction means after said actuating arm encounters one of its stops whereby said condition responsive means is effective' to continue its movement.

12. In a control device of the class described, a physical condition responsive means, a support plate, means for securing one end of the condition responsive means to the support plate, a spring blade secured tothe other end of the condition responsive means, an actuating arm, a spring hinge secured to the support plate and actuating arm and having. frictional engagement with opposite sides of said spring blade, said condition responsive means effective upon an initial operation thereof to rotate said actuating arm about said spring hinge thru the medium of said spring blade, stop means for limiting the rotative movement of said actuating arm, said spring blade effecting a frictional slipping movement between said friction means after said actuating arm encounters either of its stops whereby said condition responsive means is effective to continue its movement without straining the same, means forv adjusting the frictional effort of the friction means upon the spring blade and for eliminatingrelative lost motion of the spring blade with the friction means, and control means actuated by the movement of the actuating arm.

13. A control device comprising a physical condition responsive means, a pivoted actuating arm, a pair of stops for the arm, a slip friction mechanism connecting the actuating arm to the physical condition responsive means whereby the initial motion of the physical condition responsive means initiates movement of said actuating arm, said slip friction mechanism comprising a friction block secured to the actuating arm,

friction means carried by the guide pins fastened to the actuating arm, a second friction block, said second friction block having guide holes therein thru which said guide pins extend, a spring-blade having one end frictionally slidable between the first and second friction blocks and the other end fastened to the physical condition responsive means, and an adjustable compression spring arranged between the actuating arm and the second friction block and at an angle to said guide pins whereby said spring blade is resiliently clamped between the two friction blocks and the second friction block is held against one side of the guide pins for eliminating lost motion. a

14. In a control device, a physical condition responsive means, a support plate, means for supporting said condition responsive means upon said support plate, an actuating arm pivoted to- -said.support plate, a slip friction connection actuation of said condition responsive means upon the actuating arm reaching either of its stop members, .a manual adjustable lever pivoted,

to the support plate, means for supporting at least one of the stop members upon the adjustable member whereby' the adjustment of said lever is effective to move the stop and variably adjust the extent of movement of the actuating arm, and control means operated by the movement of the actuating arm between its stops.

15. A control device of the class described comprising a physical condition responsive means, an actuating member movable in two directions, a slip friction mechanism connecting the actuating'member to the physical condition responsive means thru which motion of the physical condition responsive means is imparted to the actuating member, a first stop for limiting the travel of the actuating arm in one direction, a second stop for limiting the travel of the actuating arm first stop whereby moving the lever about its pivot changes the relative position'of the second stop to that of the first stop, to alter the length of travel of the actuating arm between the two stops.

16. A control device comprising a physical conditionresponsive means, an actuating arm, a pair of stops for the arm, a. base, a spring blade for pivoting the actuating arm for movement toward and away from the base, a slip friction mechanism connecting the actuating arm to the physical condition responsive means at a point adja-- cent the spring blade whereby motion of the physical condition responsive means is amplified and imparted to the actuating arm until the stops are encountered, a biasing spring arranged between the base and the actuating arm, and an adjusting screw threaded through the base and engaging the biasing spring, said biasing spring supplying biasing effort to the actuating arm to move it into one position in case of failure of the actuating mechanism.

17. A control device comprising,- an expansive thermal element, a relatively non-expansive thermal element, said thermal elements arranged for relative longitudinal movement, an actuating arm, a pair of stops for limiting the movement of the arm, and a slip friction mecha-'- 18. A control mechanism comprising, an elongated thermal device including a channel member having a U-shaped cross-section and bent upon itself intermediate its ends into a generally U-shape, a second .member having a coefiicient of expansion relatively different from that of the channel member, a control arm, a connecting mechanism between the thermal device and the control arm, and means for securing one end of the second member to the channel member whereby the relative deflection of the members is utilized to actuate the control arm through the connecting means. v

19. A control mechanism comprising, an elongated thermal device including a channel member formed into a U-shape, a second member having a coefiicient of expansion relatively different from that of the channel member, a control arm, a connecting means between the thermal device and the control arm, means for securing one end of the second member to the of the members is utilized to actuate the control arm through the connecting means, and means for limiting the motion of the control arm, said connecting means including a slip friction device whereby initial relative expansion of the members is imparted to the control arm and whereby the restraining effort on the thermal device exerted by said means for limiting the motion of the control arm is prevented from exceeding a predetermined amount. I

20. In a slip friction mechanism comprising, a pair of spaced friction blocks having spaced parallel flat surfaces, a friction member arranged to frictionally engage said friction blocks,

means for pivotally supporting said friction blocks for movement, means for limiting the movement of said friction blocks, and means for slidably actuating said friction member in a linear direction against the friction of said friction blocks when they encounter their limits of movement.

21, A straight line slip friction device for transmitting motion, a source ofstraight line motion, a control arm actuated through the slip friction device from the source of motion, a support for the control arm, and a pair of elements for said slip friction device, one. of said elements'arranged tofrictionally engage the other, a portion of the first of said elements resiliently connected to the source of motion, and the second of said elements resiliently connected to the support.

22. A control device comprising a physical ,condition responsive means arranged to move with substantially straight line motion, a support for the physical condition responsive means, an actuating arm, .means for limiting the movechannel member whereby the relative expansion ment or the arm, and means including a slip friction mechanism connecting the actuating arm to the physical condition responsive means whereby initial movement of said physical condition responsive means initiates movement of the actuating arm and whereby the physical condition responsive means is restrained with not more than a predetermined amount of eifort after movement of the actuating arm ceases, said slip friction mechanism including three members, one of said members being resiliently clamped between the other two and arranged to slide therebetween, said other two members being hingedly secured to the support at the same side of said one member.

23. A control device comprising a physical condition responsive means arranged to move with substantially straight line motion, a support for the physical condition responsive means, an actuating arm, means for limiting the movement of, the arm, a slip friction mechanism connecting the actuating arm to the physical condition responsive means whereby initial movement of said physical condition responsive means initiates movement of the actuating arm and whereby the physical condition responsive means is restrained with not more than a predetermined amount of effort after movement of the actuating arm ceases, said slip friction mechanism including three members, one of said members being resiliently clamped between the other two and arranged to slide therebetween, said other two members being carried by said actuating arm, and means for aligning and resiliently supporting one of said other two members with respect to the other while substantially preventing longitudinal movement therebetween.

24. A control device comprising a physical condition responsive means, a support plate, means for fastening one end of said condition responsive means on said support plate, a connector link secured to the other end of said condition responsive means, an actuating arm, friction means having at least a portion carried by said actuating arm and arranged to engage each side of said connector link, means for hingedly securing said actuating arm to said support plate, said condition responsive means effective upon an initial movement thereof to move said actuating arm about its hinge support through the medium of said connector link, and means for limiting the movement of said actuating arm, said connector link efiecting a slippage movement between said friction means after said actuating arm ceases to move in response to said limiting means, whereby said condition responsive means is effective to continue its movement.

25. A straight line slip friction device for transmitting motion, a sourceof straight line motion, a controlarm actuated through the slip friction device from the source of motion, a support for the control arm, a pair of elements for said slip friction'device, one of said elements arranged to frictionally engage the other, a portionthe actuating arm to the physical condition responsive means whereby initial movement of said physical condition responsive means initiates movement of the actuating arm and whereby the physical condition responsive means is restrained with not more than a predetermined amount of effort after movement of the actuating arm ceases, said slip friction mechanism including three members, one of said members being resiliently clamped between the other two and arranged to slide therebetween, said other two members being carried by said actuating arm, and means between the support and the actuating arm for moving the actuating arm to one of its limiting positions in the event of failure of the physical condition responsive means or the slip friction mechanism.

27. A straight line slip friction device for transmitting motion, a source of straight line motion, a control arm actuated through the slip friction device from the source of motion, a support for the control arm,'a pair of elements for said slip friction device, one of said elements ar-,

28. A control device comprising a physical condition responsive means arranged to move with substantially straight line motion, a support for the physical condition responsive means, an 'actuating arm, means for limiting the movement of the arm, a slip-friction mechanism connecting temperature changes, a control member, a slip friction connection between said thermal device and said control member for causing actuation of said control member, a stop for limiting movement of said control member by said thermal device caused by change in temperature in one direction, said slip friction connection permitting continued movement of said thermal device after engagement of said stop by said member whereby upon reversal in movement of said thermal device the control member is immediately moved in the opposite direction, said thermal device comprising first and second substantially parallel elongated members having difierent coefficients of expansion, one of said elements being fixedly secured at one'end and the other of said elements being connected to said slip friction connection, the other ends of said elements being connected together, said elements being substantially equally exposed to the fluid in said passage so as to change in temperature at substantially the same rate upon change in temperature of the medium to which the elements are exposed, whereby reversal of said control member due to unequal exposure of said elements is avoided.

30. A control device comprising a base, a physical condition responsive device having a portion thereof fixedly secured relative to the base, another portion thereof moving relative to the base upon change in value of said condition, an actuating armhinged to the base, a connector link actuated in a straight line direction by the movthe actuating arm to the physical condition responsive means whereby initial movement of said physical condition responsive means initiates movement of the actuating arm and whereby the physical condition responsive means is restrained with not more than a predetermined amount of effort after movement of thev actuating arm other, and means for adjusting the resilient member to vary the amount of restraining efiort of the slip friction mechanism on the physical condition responsive means.

29. In a. control mechanism of the class described, an elongated thermal device adapted for mounting in a passage for fluidsubject to rapid able portion of the condition responsive device, a pair of friction blocks carried by said actuating arm and engaging opposite faces of said connector link, and resilient means urging said friction blocks against said connector link.

31. A control device comprising a base, a physical condition responsive device having a portion thereof fixedly secured relative to the base, another portion thereof moving relative to the base upon change in value of said condition, an actuating arm hinged to the base, a connector link actuated in' a straight line direction by the movable portion of the condition responsive device, a

pair of friction blocks carried by said actuating arm and engaging opposite faces of said connector link, resilient means urging said friction blocks against said connector link, and hinge means compensating for the difference between the arcuate motion of the friction blocks about the pivot of the actuating arm and the straight line motion of the connector link whereby the friction blocks and connector link remain aligned- WILLIAM CHRISTIANSEN. 

